Band grinding tool for rounding edge portions of blades for compressor and turbine plants

ABSTRACT

A band grinding tool for rounding the edge portions of blades for compressor and turbine plants is proposed wherein the device for fastening the workpiece to be machined and for feeding it to the grinding area comprises a support connected to the bed through an elastic link, the support being capable of moving in the direction of the transverse feeding and carrying a movable head connected to it, and containing a means to accomplish the longitudinal traverse of the tool profile along the surface of the profile cam, the means being used for rocking the head with respect to the support to accomplish the longitudinal traverse of the workpiece along the grinding band supported in the machining area by the support cam.

[ Jan. 7, 1975 Unite States atent n91 Tashker Primary Examiner-A1Lawrence Smith EDGE PORTIONS OF BLADES FOR Assistant Examiner-NicholasP. Godici COMPRESSOR N TURBINE PLANTS Attorney, Agent, or Firm-Waters,Roditi, Schwartz &

Nissen 1 BAND GRINDING TOOL FOR ROUNDING a s .n we MU k "8 M v Tk m2 3mm .m m .1 K E O I n e v n I 1 6 7 .l.

U.S.S.R.

ABSTRACT 22 Filed: Jan. 2, 1973 21 Appl. No.: 320,587

rein the device for fastening the workpiece to be machined and forfeeding it to the grinding area comprises a support connected to the bedthrough an elastic link, the support being capable of moving in the di-[52] US. 51/144, 51/148 [51] Int. B2411 21/16 [58] Field ofSearch.......... 51/135 R,l41, 142, 143

rection of the transverse feeding and carrying a movable head connectedto it, and containing a means to References Cited accomplish thelongitudinal traverse of the tool profile UNITED STATES PATENTS alongthe surface of the profile cam, the means being 51/144 used for rockingthe head with respect to the support 5 4 to accomplish the longitudinaltraverse of the workpiece along the grinding band supported in themachining area by the support cam.

2,606,406 8/1952 Muel1er................................ 3,528,2009/1970 Allen FOREIGN PATENTS OR APPLICATIONS 4 Claims, 3 Drawing FiguresPatented Jan. 7, 1975 2 Sheets-Shem 1 Patented Jan. 7, 1975 2Shoots-Sheet m BAND GRINDING TOOL FOR ROUNDING EDGE PORTIONS OF BLADESFOR COMPRESSOR AND TURBINE PLANTS The present invention relates togrinding tools, and more particularly, to band grinding tools forrounding edge portions of blades for compressor and turbine plants.

The invention can most successively be used for dimensional rounding ofvariable-radius spatial curves in a direction lengthwise of the edgeportions of blades for gas turbines. The blades machined on the tool maycontain one flange (lock), two flanges or have no flanges at all. It isalso possible to machine the edge portions of blades having rectilineargenerants and being in compliance with the linear law of changing thecurve radius.

The tool can find a wide application in the aircraft engine buildingindustry, as well as in general engineering for machining the edges ofblades for stationary gasturbine installations, compressors, etc.

At present the machining rounding the leading and the trailing edges-isone of the most urgent problems in the engine building industry, sincethe engine efficiency as well as the strength of the blade proper, i.e.the service life of the engine, in the long run, depends on the qualityof the edges.

The rounding of the variable-radius spatial curves in a directionlengthwise of the edge portions of blades for gas-turbine engines iscarried out at present everywhere manually with the aid of grindingblocks, which fails to provide the required geometrical rounding, beingoften accompanied by burned edges and inflicting professional diseaseson the workmen, yielding at the same time a low labour productivity.

Numerous attempts to mechanise the rounding operation by grinding thevariable-radius spatial curves in a direction lengthwise of the edgeportions of blades failed to produce positive results and did not findapplication due to the following reasons.

While machining separately the tip profile and the edges, warpage of thetip and its climb from the bases inevitably occur in the course ofgrinding which makes it impossible to use these bases while machiningthe edges (a forcible bending of the tip in order to remain the bases isnot allowed).

The device for grinding the leading and the trailing edges of blades bymeans of an abrasive wheel shown in the book by M. F.ldzon MechanicalMachining of Blades for Gas-Turbine Engines, Moscow, 1963, FIGS. 5, 8,p. 177, has the same disadvantage, and some others, too:

a. the grinding by an abrasive wheel causes, as a rule, the burning ofthe blade (no matter what kind of cooling is applied), microcracks and,consequently, reduces the service life of the blade;

b. while grinding by an abrasive wheel, the workpiece sticks as it turnsaround the axis of the edge centres, receiving a shock and being bent.

The band grinding tools also described in the book by M. F.1dzonMechanical Machining f Blades for Gas- Turbine Engines, Moscow, 1963,pp. 195-21 I, employing a narrow abrasive band are utilized to machinethe tip of the blade together with the edges all around per onepositioning of the workpiece, i.e., they are dispensed with thementioned disadvantages, but have a complex system of two matchedcutting profiles or complex spatial cutting profiles of the entire tipof the blade whose finishing is complicated, therefore the tools have sofar failed to provide a suitable workpiece with machined edges. Besides,all these tools possess such essential disadvantages, as:

a. since it is impossible to maintain an uninterrupted grinding, themachining of edges on them is accompanied by a considerable wear of theabrasive band and its possible breaks; one has also to expect thesticking and bending of the blade tip by the band;

b. their efficiency is small in machining the edges while they employ anarrow band;

c. it is impossible to machine the slant edge portions of the bladehaving high flanges.

The machining of the edge portions of blades by blade tools (planartool, milling cutter) described, for example, in US. Pat. No. 2,74l,l64,issued Apr. 10, 1956, Methods of and Apparatus for Working Materialsdoes not ensure the machining of edge in a direction running the entirelength of the edge and its slant portion, since for this purpose it isnecessary to have a section of considerable length to accommodate thetoo]. This disadvantage becomes more manifest while machining bladeswhich have high flanges (locks). Besides, due to low strength of thecutting tool, this method of machining cannot practically be used forrounding the edges of the turbine blade fabricated from heat resistingalloys, possessing a high hardness and viscosity. The quality of themachined surface obtained in the course of blade machining is of lowstrength and poor geometrical characteristics, and in order to improvethem a finish machining is required.

The only tool producing dimensional rounding by grinding the leading andthe trailing edge portions of blades for compressor and turbine plantsis the blade grinding tool developed, constructed and utilized in theUSSR for rounding the edge portions of the blades having rectilineargenerants (Authors Certificate No. 195,922 issued in the USSR on Jan.21, 1966).

installed on the machine bed of the known tool is a device for fasteningthe workpiece to be machined and for feeding it to the grinding area,and a mechanism for moving the grinding band being supported in themachining area by a support cam. The support cam is lo cated in the bed,and in the course of grinding it moved reciprocatingly in the directionperpendicular to the surface to be machined to perform the interrupted(vibrational) grinding.

The rounding of the edge portion on the known machine tool isaccomplished while the blade rotates with respect to the rectilinearaxis of the rounding radii, and in this case the working surface of thesupport cam is flat.

Since the known machine tool contains no mechanism for profiling, itcannot perform the rounding of variable-radius spatial curves in a.direction lengthwise of the edge portions of the blades having acurvilinear axis of the rounding radii.

The principal object of the present invention is to provide a bandgrinding machine which ensures the machining of the variable-radiusspatial curves in a direction lengthwise of the edge portions of blades,including the edges with rectilinear generants.

Another object of the invention is to provide a machine tool formachining the edge portions of the blades having high locking flanges.

Still another object is to provide a tool which can use a wide abrasiveband for machining the edges.

Besides, an object of the invention is to provide a tool capable ofmachining the edges by means of interrupted grinding which increases thestrength of the band, and due to decrease of heat intensity of thecutting process, contributes to a higher quality of the machinedsurface.

These and other objects of the invention are accomplished by means ofthe band grinding tool having a bed which supports therein a device forfastening the workpiece to be machined and for conveying it to thegrinding area, and a mechanism for moving a grinding band which isretained in the machining area by a support cam located in the bed. Thecam, during the course of grinding, performs reciprocating movements inorder to accomplish an interrupted grinding sequence wherein, accordingto the invention, the device for fastening the workpiece to be machinedand for feeding it to the grinding area contains a support mounted onthe bed and which is capable of moving in the direction of transversefeeding of the workpiece. The device carries a movable head with anattachment for fastening the workpiece and a tool profile, and includesa drive for effecting their synchronous rotation so as to be able tofeed the workpiece angularly, with the tool profile for the transversefeeding of the workpiece being constantly pressed against the profilingcam mounted on the bed, the latter of which is flexibly connected to asupport to ensure a longitudinal traverse of the tool profile along thesurface of the profiling cam, and having a means for rocking the headwith respect to the support through a movable connection therebetweenfor carrying out a longitudinal traverse of the edge to be machinedalong the grinding band while being supported in the grinding area bythe support cam.

This made it possible to machine the variable-radius spatial curves in adirection lengthwise of the edges (including those with rectilineargenerants) by means of a wide abrasive band while accomplishing theinterrupted abrasive band grinding. The machine tool is capable ofmachining the edge portions of the blades having high locking flanges orwithout the latter.

According to the invention, it is most expedient to have a movableconnection between the support and the head in the form of a common axlemovable in the support and having a head and a lever fastened to it, thelatter being connected to the means for rocking the head.

Such a design provides for a very simple rocking of the head and areliable protection of the movable components and units againstimpurities and abrasive particles, thus contributing to improvedreliability and a longer service life of the tool.

It is expedient to make provision for moving the support in thedirection of the transverse feeding of the workpiece by means of a pivotconnecting the support with the bed, the pivot axle being moved at somedistance and held parallel to the common axle of the support and thehead.

Such a design is easily protected against impurities, lends itself to beindustrially produced and can be fabricated with a high degree ofaccuracy. This improved the accuracy of the tool and the stability ofits characteristics in the process of operation.

It is advisable to construct the means for rocking the head with respectto the support in the form of a linkand-cam mechanism wherein one end ofthe link interacts with the lever connected through an axle to the head,the other end of the link is adapted to take up the constant-amplitudeoscillations, and its rocking axle is located on the slide moving alongthe link for changing the rocking amplitude of the head in the course ofoperation according to the pre-set law to be determined by theconfiguration of the edge to be machined and set by the cam profile.

Owing to the fact that the said means is so constructed, a compact rigiddesign is obtained which provides highly accurate movements as a resultof the rigid kinematic connection of its moving components and units;the small size and a low weight of such a construction make it possibleto increase to a maximum the number of head rockings limited only by theinertia of its mass, thus improving the quality of the machined edgesurface.

Other features and advantages of the present invention will become moreapparent from the detailed description of a specific example withreference to the accompanying drawings wherein:

FIG. 1 is a kinematic diagram of the tool, according to the invention;

FIG. 2 is a basic diagram of the blade movement while rounding its edgeportion on the tool, according to the invention;

FIG. 3 is a sectional view taken on line II-Il of FIG. 2.

The proposed band grinding tool for rounding the edge portions of bladesfor compressor and turbine plants comprises the follwing mainassemblies: a bed I (FIG. I) installed on which there is the device forfastening the workpiece to be machined and for feeding it into thegrinding area, and the mechanism for moving the grinding band.

The device for fastening the workpiece to be machined and for feeding itinto the grinding area contains a support 2 mounted on the bed I bymeans of a pivot 3 making it possible for it to move in the direction oftransverse feeding of the workpiece. Movable on the support 2 is thehead 4. The movable connection between the support 2 and the head 4isconstructed in the form of a common axle 5 installed in the support 2in tapered bearings.

In this case, the axle of the pivot 3 is spaced some distance apart fromthe common axle 5 and is held parallel to this axle 5. Mounted on thehead 4 is the device 6 for fastening the workpiece and the tool profile7, as well as the drive for synchronous rotation of the blade 8 to bemachined and the tool profile.

The mechanism for moving the grinding band contains a roller 9 leadingthe abrasive band 10 by means of a V-belt drive and being rotated by theelectric motor II. Mounted on the bed I is the profile cam 12 supportingthe grinding band 10 in the machining area. The working surfaces of thetwo cams l2 and 13 are cylindrical, their axes coincide in the workingposition, and their radii difference is equal to the difference ofdistances from appropriate points of the machined surface of the blade 8and the surface of the tool profile 7 to their rotation axes O and 0,,with the thickness of the band 10 being subtracted, provided the toolprofile 7 is thicker than the edge of the blade 8. If the tool profile 7is thinner than the edge portion of the blade 8, the

thickness of the band is added (algebraically) to the difference soobtained. To compensate for the wear of the band 10, the profile cam 12can be moved by means of the adjusting screw 14.

The support cam 13 is capable of moving reciprocatingly while grindingin the direction perpendicular to the axis of its cylindrical workingsurface by means of an eccentric 15 installed on the shaft 16 which isrotated by the V-belt drive from the electric motor ll connected to theband 10 performing, as a result, the interrupted grinding. The value ofthe eccentricity e, i.e., the displacement amplitude of the support cam13 can be changed in the course of adjustment.

To form a transverse feeding of the workpiece, the tool profile 7 isconstantly pressed against the profile cam 12 installed on the bed I bymeans of an elastic connection linking the support 2 and the bed I, andconstructed in the form of a tension spring 17.

The blade 8 is fastened to the attachment 6 which is capable of rotationabout the axle l8 and of movement along the guides 19 perpendicular tothe working surface of the support cam 13. When bringing the blade 8 tothe fixing pins (not shown in the Fig.) fastened to the bed I anddetermining the initial position of the blade 8 (they are pressedagainst the trough surface of the edge portion of the blade locatedimmediately at the edge to be machined), all the movable elements of theattachment are fixed in the positions they occupy, after which themachining cycle can be started.

The shaft 20 of the attachment 6 installed on the head 4 is rigidlyconnected to the parallel shaft 21 which rotates the tool profile 7 bymeans of a steel band 22 fastened to the drums 23 of equal diameters.

For a synchronous rotation of the tool profile 7 fas tened to the shaft21 and the blade 8 connected to the shaft 20 of the attachment 6 forfastening the blade, to forman angular feeding, use is made of thepinion 24, toothed sector 25 and pinion 26 fastened to the shaft 27. Thepinion 26 is rotated by means of a rack 28 installed in the support 2.The rack 28 can move reciprocatingly under the effect of the arm 29rotated about the axle 30 by means of the flat cam 31 (which sets thelaw of varying the speed of rotation of the blade 8 while machining theedge) and has for this purpose a roller pusher 32 and a spring 33 forreturning the rack 28.

To form a longitudinal traverse of the tool profile 7 on the surface ofthe profile cam 12, the support 2 is equipped with a means which rocksthe head with respect to the support for the purpose of accomplishingthe longitudinal traverse of the edge portion of the blade 8 along thegrinding band 10 supported in the machining area by the support cam 13.

The said means is a link-and-cam mechanism whose cam 34 is designed tovary the rocking amplitude of the head 4 and is fixed on the same shaftas the flat cam 31 and the worm wheel 35 rotated by the worm 36.

The worm 36 is fastened to the shaft 37 connected through a telescopiclink 38 installed in the bed I to the reduction gear 39 of the feed andtraverse drive by means of which the motion from the electric motor 40is imparted (through the pinions Z Z Z Z Z the switch-over unit ofpinions Z and Z Z and Z the shaft 41 and the pivot link 42) to thesupport 2.

To form the rocking amplitude of the head 4, use is made of a camgenerator consisting of a drum cam 43 which is rotated through thepinions 44 and 45, with the latter being fastened to the shaft 37, and amovable frame 46 interacting with the drum cam 43 through the pin 47located in the curvilinear groove of the drum cam 43.

The movable frame is located in the support 2 with the aid of thejournals 48 and carries the link whose end 49 is pivotably fastened toit, for the movable frame 46 to take up the oscillations of constantamplitude from the drum cam 43. The other end 51 of the link 50 has tworollers, one of them being located in the fork of the bracket 52 whichserves as the lever connected to the head 4, and the other roller in thestationary guides 53 of the support 2 being used to take power load offthe link 50. The connection between the bracket 52 and the head 4 iseffected in the form of stationary link between the head and the commonaxle 5 which, in turn, is rigidly connected to the head 4 to impart therocking of the link 50 to the head 4.

The link 50 has a movable slide 54 with its rocking axle in the form ofjournals 55 located in the fork 56 of the slide 57 installed on thesupport 2.

The slide 54 can move reciprocatingly along the link under the effect ofthe arm 58 rotating about the axle 30 by means of the cam 34, for whichpurpose the fork 56 has on its end a movable link 59 connected to theend of the arm 58, and the power circuit of the cam 34 is locked by thespring 60 supporting the slide 57.

Thus, the variation of the rocking amplitude of the head 4 takes placein the course of operation in accordance with the pre-set law which isdetermined by the configuration of the edges to be machined and set bythe profile of the cam 34.

Employed in the tool is a mechanism for tensioning the grinding bandwhich makes it possible:

to provide a considerable effort of tensioning the grinding band sincethe employed band has a width equal to or a little larger than thelength of the edge to be machined, and 4 to have a minimal inertia toavoid tearing the band and to improve the conditions for the interruptedgrinding.

Accordingly, the mechanism for tensioning the grinding band comprises aguiding roller 61 rotating loosely on the end of the shaft 62, a tensionroller 63 rotating on the axle 64 fastened by means of a bracket 65 andheld parallel to the shaft 62, an arm 66 mounted on the opposite end ofthe shaft 62 with a tension spring 67 fixed to one end of the shaft andwith a rod 68 fixed to the other end, the rod being pivotably connectedto the rack 69. A self-switchingoff oil damper 70 is fastened to the arm66. The other end of the spring 67 is fastened to the bed I.

For tensioning the spring 67 (while replacing the band 10), the pinion Zbeing engaged with the rack 69 and fastened to the same shaft 71 as thepinion Z can be rotated with the help of the electric motor 40 whileswitching over the unit of pinions Z Z, by means of the handle 72. Therack 69 is provided with a springloaded latch 73 serving to retain thespring 67 in a tensioning position for which purpose there is a stop 74fastened to the bed I. The handle 72 has a stop 75 which, while placingthe unit of pinions Z Z to the operating position (engagement with thepinion Z8). depresses the latch 71 releasing the rack 69. Theselfswitching-off oil damper 70 has a piston 76 whose rod is fastened tothe arm 66, and a cylinder 77 which has two cavities: one being locatedunder the piston 76 and the other serving as an oil tank (the cavitiesare interconnected by means of a non-return ball valve 78 and an orificelocated at the bottom of the cylinder 77). The bottom of the cylinder 77contains a spherical well and a bar 79 located in the middle. The bar 79has a longitudinal hole containing a cylindrical pin 80 installed in thevertical wall of the bed I. The spherical plate 81 is mounted on thehorizontal wall of the bed I under the bottom of the cylinder 77. Thecylinder 77 is lifted from the horizontal wall of the bed (and,consequently, from the spherical plate 81) by the spring 82; its travelis restricted by the displacement of the pin 80 in the longitudinal holeof the bar 79,

FIG. 2 shows the diagram of machining (rounding by grinding thevariable-radius spatial curve in a direction lengthwise of the edgeportion of the blade to be accomplished by the tool of the proposeddesign.

In FIG. 2:

O is the horizontal axis of rotation of the blade 8; the rotation aboutthe axis provides for the feeding of the workpiece to the tool profile(the direction of movement of the blade 8 about the axis is indicated bythe arrows B-B);

K is the principal vertical axis of traverse about which the edgeportion of the blade 8 is traversed, this being accomplished along itsgenerant on the working surface of the support cam 13 having theabrasive band located on the latter, with the direction of the bandmovement being indicated by the arrow a;

N is an auxiliary vertical axis of traverse, the rocking about which isnecessitated by the rocking of the blade 8 about the axis K, Le. in thecourse of the traverse the axis K is being displaced occupying thepositions K,

. K, etc.

To provide conditions for traversing the blade 8 along the workingsurface of the cam 13, it is necessary that the working surface beconvex(cylindrical for the sake of simplicity, as fabrication is concerned)since the abrasive band does not fully adjoin to a concave surface (inthe mid-portion of the concave support cam), and the grinding isaccomplished irrespective of the'cam shape contributing to a loweraccuracy of machining. As a result, the radius R of the cylindricalworking surface of the support cam 13 must be selected to be of maximumsize (to reduce the rocking angle of the blade 8 about the axis K in thecourse of traverse), but it must be smaller than the minimal curvatureradius of the edge surface to be machined in the longitudinalcross-section.

Thus, the rounding of the edge is accomplished while rockingsimultaneously the blade 8 with respect to the axis 0, K and N. (Thepositions taken up in this case by the blade 8 are indicated by thedashed line). Evidently, the amplitude of rockings of the blade 8 withrespect to the axis K (the amplitude of rockings about the axis Ncoincides with the amplitude of rockings about the axis K) must beconsiderably greater than the amplitude of rockings about the axis 0, toensure highquality machining (absence of finish, improved cooling,etc.). In this case, grinding is performed in a quickmoving point ofcontact (the speed of its travel depends not only on the frequency ofrockings of the blade 8 about the axis K, but on the difference betweenthe radius R and the curvature radius of the edge in its crosssection:the smaller the difference, the higher the speed of the contact pointtravel along the edge. In this way, it is possible to achieve such highspeeds of the contact point travel (grinding) along the edge, as cannotbe obtained otherwise. It means that with a similar quality ofmachining, for example, while obtaining a similar finish of the edge,the productivity of the proposed tool (its machining diagram is shown inFIG. 2) will be considerably higher than any others.

The tool (its kinematic diagram is shown in FIG. I) operates in thefollowing manner.

In the tool prepared for work, the abrasive band 10 occupies theoperating position on the rollers 9, 63, 61, and on the working surfaceof the cam 13; the kinematic traversing circuit is closed by the handle72, with the pinion Z being engaged with the pinion Z The blade 8 isinstalled in the attachment 6 and moves towards the cam 13 (turningabout the axle l8 and along the guides 19) so that the surface of theedge trough would contact the two stops (not shown in FIG. I); in thisposition all the movable elements of the attachment 6 are fixed ensuringthe positioning of the blade 8 along the edge to be machined.

In the tool prepared to start work, the spring 17 presses the toolprofile against the surface of the profile cam 12 turning the support 2on the pivot 3 with respect to the bed I.

On starting the electric motor II, the guide roller 9 sets the abrasiveband 10 in motion (the direction of travel of the band is indicated bythe arrow a); the motor rotating the eccentric 15 imparts reciprocatingmotion along the arrow B to the support cam 13 performing theinterrupted grinding. The power is transmitted from the electric motorthrough a V-belt drive.

The electric motor 40 is switched on to provide power for the feedingand traversing. The direction of travel of the mechanisms are shown inthe Figures by arrows to give a better presentation. Its rotation istransmitted to the support 2 by means of the reduction gear 39 (toothedwheels Z, Z through the pivot link 42 and the telescopic connection 38.The worm 36 and the drum cam 43 rotate therewith, the latter being setin motion by means of the pinions 45 and 44. The worm 36 rotates thefiat earns 31 and 34 with the help of the worm wheel 35. The flat cam 31acts by means of the roller pusher 32 on the arm 29 (rotated on the axle30) which lifts therack 29 (it is lowered by the spring 33). The rack 28turns the pinion 26 resulting in a simultaneous rotation (in the samedirection and at the same speed) of the blade 8 and the tool profile 7,since the motion is imparted by the toothed sector 25 to the pinion 24fastened to the shaft 21 and then further by means of the band 22fastened to the drums 23 to the shaft 20. Thus the feeding of the blade8 (its edge) to the cutting profile is ensured. Simultanesously, therotating drum cam 43 rocks the movable frame 46 in the journals 48 bymeans of the pin 47. As a result, the end 49 of the link 50 pivotablyfastened to the frame rocks together with the slide 54 about thejournals 55 of the latter. The other end of the link located in the forkof the bracket 52 (fixed to the axle 5 of the head 4) while moving turnsthe head 4 rocking it in the bearings of the support 2 accomplishing thetraverse of the edge of the blade 8 along the surface of the cam 13 (orthe tool profile 7 along the surface of the profile cam 12).

The curvature of the edge surface of the blade 8 in the variouscross-sections passing through the axis of rotation O is different, andwhile machining, it is necessary to maintain the speed of thelongitudinal traverse of the blade (the speed of travel of the contactpoint between the abrasive band and the surface of the blade 8 to bemachined).

To make provision for this, the cam 34 rotates the arm 58 about the axle30 moving the slide 54 along the link 50, with the slide 57 supportingthe slide 54 being also moved. The travel of the slide 54 changes theratio between the arms of the link 50 whose end 49 together with themovable frame 46 performs rockings of constant amplitude and cycle.

As a result, the amplitude of the rockings of the upper end 51 of thelink 50 changes, maintaining a constant cycle of rockings, i.e. therocking speed of the head 4 changes in compliance with the change in thecurvature of the surface of the blade 8 and the travelling speed alongthe edge of the contact point between the surface to be machined and theabrasive band 10 remains constant while the blade 8 rotates.

When the arm 29 performs one double rocking with one revolution of thecams 31 and 34, the blade 8 returns to the initial position and the toolstops indicating the end of the machining operation.

The replacement of the abrasive band 10 is carried out in the followingmanner. The pinion Z is brought into engagement with the pinion Z bymeans of the handle 72. The electric motor 40 by rotating the pinion Zby means of the pinions Z Z Z shifts the rack 69 turning the arm 66 andalso the bracket 65 with the tension roller 63 and tensioning the spring67 until the spring-loaded latch 73 passes over the stop 74. In sodoing, the piston 75, 76 of the self-switching-off damper 70 comes outof the cylinder 77. Having positioned the abrasive band 10, the handle72 is lowered; its stop 75 is pressed against the latch 73 releasing thespring 67 which strains the abrasive band 10. To avoid the tear of theabrasive band 10, use is made of the selfswitching-off damper 70. Thespring 67 thrusting the piston 76 into the cylinder 77 makes the oilpass through the orifice located at the bottom of the cylinder. Theexcess pressure in this case shifts the cylinder 77 in the wake of thepiston 76 compressing the spring 82 (which is weaker than the spring 67)until the bottom of the cylinder 77 rests on the spherical plate 81fastened to the bed I. The travelling speed of the piston 76 isdetermined afterwards by the diameter of the orifice in the cylinder 77.When the tool operates, the damper 70 should not effect the mobility ofthe tensioning system of the abrasive band 10. This is achieved due tothe spring 82 which lifts the cylinder 77 clear of the spherical plate81 (the lift is restricted by the cylindrical pin 80 located in thelongitudinal hole of the rod 79 of the cylinder 77).

To eliminate the resistance to the piston 76 while coming out of thecylinder 77 (when tensioning the spring 67), use is made of thenon-return ball valve 78.

The tool constructed according to the described kinematic diagram madeit possible to accomplish a dimensional rounding of the edge portions ofblades rendering a high-quality surface and increasing the operationalreliability and service life of the edge portion of blades.

Being rather self-contained, with no complex hydropneumatic andelectropneumatic components, the tool having all the open assembliesmade pivotable, with a minimal number of transitional pairs (whichcontributes to a better protection of the construction against 10impurities) ensures a highly reliable operation, simple maintenance andadjustment.

The arrangement of the tool profile and the workpiece to be machined onone head with a minimal number of conjugated components ensures a highaccuracy of operation irrespective of the wear of drive mechanisms andguides, and also contributes to a longer service life of the tool.

What is claimed is:

l. A band grinding tool for rounding the edge portion of workpieces,such as blades for compressor and turbine plants within a grinding areacomprising: a bed; a mechanism for moving a grinding band installed onsaid bed; a device for fastening the workpiece to be machined and forfeeding it to the grinding area, the device being installed on said bed;a support cam located in said bed retaining the grinding band in thearea of machining the blade during the course of grinding, meansperforming reciprocating motions to said support cam to accomplishinterrupted grinding; said device for fastening the workpiece to bemachined and for feeding it to the grinding area comprising a movablehead with an attachment for fastening the workpiece and a tool profile;a support mounted on said bed including means for moving in thedirection of the transverse feeding of the workpiece and carrying saidmovable head, the support being connected through an elastic link tosaid bed; a profile cam mounted on the said bed; a drive for effectingsynchronous movement of said attachment for fastening the workpiece andof the tool profile, the drive imparting angular feeding movement to theworkpiece; said tool profile being constantly pressed against saidprofile cam to accomplish the transverse feeding of the workpiece, saiddrive including means to form a longitudinal traverse of the said toolprofile toward the surface of the said profile cam, said last-mentionedmeans rocking said head with respect to said support through a movablelink therebetween for the longitudinal traverse of the workpiece edgewith-respect'to the grinding band.

2. A tool as set forth in claim 1 wherein the connection between thesupport and the head is constructed in the form of a common axle movablyinstalled in the support with a head and a lever fastened to the axle,the lever being connected to the means for rocking the head.

3. A tool as set forth in claim 1 wherein the means for rocking the headwith respect to the support is a linkand-cam mechanism wherein one endof the link interacts with a lever connected to the head through acommon axle, and the other end is adapted to take up constantamplitudeoscillations, with a link-rocking axle being constructed on the slidemoving about it for changing the amplitude of the head rocking in thecourse of operation according to the configuration of the edge to bemachined and adapted to be set by a cam profile.

4. A tool as set forth in claim 3 wherein said means for moving thesupport in the direction of the transverse feeding of the workpiece is apivot connecting the support with the bed, the axle of the pivot beingspaced at some distance and held parallel to the common axle of thesupport and the head.

1. A band grinding tool for rounding the edge portion of workpieces,such as blades for compressor and turbine plants within a grinding areacomprising: a bed; a mechanism for moving a grinding band installed onsaid bed; a device for fastening the workpiece to be machined and forfeeding it to the grinding area, the device being installed on said bed;a support cam located in said bed retaining the grinding band in thearea of machining the blade during the course of grinding, meansperforming reciprocating motions to said support cam to accomplishinterrupted grinding; said device for fastening the workpiece to bemachined and for feeding it to the grinding area comprising a movablehead with an attachment for fastening the workpiece and a tool profile;a support mounted on said bed including means for moving in thedirection of the transverse feeding of the workpiece and carrying saidmovable head, the support being connected through an elastic link tosaid bed; a profile cam mounted on the said bed; a drive for effectingsynchronous movement of said attachment for fastening the workpiece andof the tool profile, the drive imparting angular feeding movement to theworkpiece; said tool profile being constantly pressed against saidprofile cam to accomplish the transverse feeding of the workpiece, saiddrive including means to form a longitudinal traverse of the said toolprofile toward the surface of the said profile cam, said last-mentionedmeans rocking said head with respect to said support through a movablelink therebetween for the longitudinal traverse of the workpiece edgewith respect to the grinding band.
 2. A tool as set forth in claim 1wherein the connection between the support and the head is constructedin the form of a common axle movably installed in the support with ahead and a lever fastened to the axle, the lever being connected to themeans for rocking the head.
 3. A tool as set forth in claim 1 whereinthe means for rocking the head with respect to the support is alink-and-cam mechanism wherein one end of the link interacts with alever connected to the head through a common axle, and the other end isadapted to take up constantamplitude oscillations, with a link-rockingaxle being constructed on the slide moving about it for changing theamplitude of the head rocking in the course of operation according tothe configuration of the edge to be machined and adapted to be set by acam profile.
 4. A tool as set forth in claim 3 wherein said means formoving the support in the direction of the transverse feeding of theworkpiece is a pivot connecting the support with the bed, the axle ofthe pivot being spaced at some distance and held parallel to the commonaxle of the support and the head.